This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A072235 #7 Mar 30 2012 17:36:39 %S A072235 -240,-164,-87,-12,66,141,218,295,374,451,530,607,684,760,837,912,989, %T A072235 1066,1145,1222,1301,1378,1456,1531,1607,1682,1759,1835,1910,1986 %N A072235 Years of recorded observations of Comet Halley. %C A072235 This sequence is not well-defined for many reasons (negative years are ill-defined; calendars change often, so when does a year begin?; what does "observed" mean?; what if the comet was observed both at the end of one year and at the beginning of another, as in 1985/1986?; etc.). - _N. J. A. Sloane_, Jun 24 2007 %C A072235 The first four terms given are years B.C., others are A.D. I do not know if these years necessarily coincide with actual years of perihelion. Some sources and these numbers indicate that the comet's period varies. These years are taken directly from the U.S. National Air and Space Museum link. %H A072235 National Air and Space Museum, <a href="http://www.nasm.si.edu/ceps/etp/comets/comet_history.html">Exploring Comets - Historical Records</a> %H A072235 N.A.S.A., <a href="http://nssdc.gsfc.nasa.gov/planetary/factsheet/cometfact.html">Comet Fact Sheet</a> %H A072235 Wikipedia, <a href="http://www.wikipedia.org/wiki/Comet+Halley">Comet Halley</a> %Y A072235 See A100748 for another version. %K A072235 sign %O A072235 1,1 %A A072235 _Rick L. Shepherd_, Jul 05 2002